Muffle furnace



W. G. BRIDGE ET AL MUFFLE FURNACE oct'. 4, 1921. 1,644,101

Filed Anm '17 192s 2 sheets-sheet l oct'. 4, 1927. [1,644,107

v W. G. BRIDGE ET AL MUF'FLEy FURNACE Filed April 1'7 1926 2 Sheets-Sheet v f7-zwei at@ 71? Waite?" jra' WaZZL'a/? 0.2%

Patented Oct. 4, 1927.

UNITED STATESN PATENT oFFicE.

WALTER G'. BRIDGE, OF NEWTON, AND WILLAli/I A.. PEBVIER, OF VIATERTOWN, 1VJIAS- SACHUSETTS, ASSIGNORS TO DR. CHARLES E. PARKHURST, OF SOMERVILLE,1VIAS- SCHUSETTS.

MUFFLE FURNACE.

Application led April 17, 1926. Serial No. 102,659.

This invention relates to electric heating devices, and more particularly to furnaces of the muiile type which are designed to bake porcelain or the like. An object of the 1nvention is the provision of a furnace of the above indicated type for use in making artificial dentures, which will be adapted to low cost production, may be easily repaired and will be eliicient and convenient in use. A salient feature of the invention is the arrangement of the muflie, whereby the lining and heating elements may be readily renewed, whereby the heat may be uniformly and efliciently supplied to the heating chamber and the material therein, and whereby the muilie may be easily cleaned.

The above and further objects of the invention will become apparent to those skilled in the art upon a reading of the subjoined description and claims in conjunction with the accompanying drawings.

In the drawings,-

Fig. 1 is a top plan view of the improved muflie furnace;

Fig. 2 is a side elevation of the saine;

Fig. 3 isa bottom view of the cover;

Fig. 4 is a vertical section on line iwi of F ig. 3; Y Fig. 5 is a detail view of the m'ufde;

Fig. 6 is a section on line 6-6 of Fig. 5;

Fig. 7 is a detail sectional view; and

Fig. 8 isa diagrammatic view of the inutile plate assembly.

In its preferred embodiment the muiiie furnace illustrated in Figs. 1 and 2 comprises a base l provided with supporting legs 2 at its corners. Above the base is located a substantially rectangular bed plate 3 containing a rheostat of standard type, which is actuable by the handle 5. The furnace proper is located above the bed plate and comprises an outer casing 6 of metal, such as aluminum, with a suitably disposed cover 7, said cover being secured to a pivotally mounted rod 8 provided with an extending handle 9. The rodS is secured by pivot 11 to a collar 12 rotatably mounted on upright 10, which comprises a rod extending' upwardly from one of the legs 2 of the base member. During use of the device the rod 8 and cover 7 may be moved by means of the handle 9 so that the cover is swung around pivot 11 or collar 12, whereby the cover may be located at any con-- venient point in a substantially inverted position. j

The muie or furnace proper comprises a receptacle 13 of heat insulating material, such as clay, disposed with the supporting ring 418 which has a flange 19 engaged with the upper edge of casing 6. rhe receptacle has a suitable number of slightly tapered Vfaces each of which'abuts a muftle plate 16. Muiiie plates 16 comprise a lining'for the central chamber l5 and are preferably arranged in hexagonal relation as-illustrated more particularly in Fig. 5 `and may consist of any suitable refractory material which is also adapted to provide proper lelectric insulation.

Electric energy is received from an eX- ternal circuit through the binding posts 23 and the rheostat in the base, and the leads 20 of platinum wire are Vdetachably connected to portions of the radially disposed, insulated supports 23 which are in turn connected to the rheostat. Leads 20 comprise extensions of the looped wires embedded in adjoining muflie plates 16a and 16h. The intermediate muftle plates are each nprovided with a similar looped wire 21, preferably of platinum 'or a platinum alloy, a portion 22 of this wire projecting from the vertical edges of each of the plates in juxtaposed relation with similar wires upon adjoining plates, these projectingwire portions being twisted around one another so that a continuous circuit is provided between lead wires 20 through each of the muflie plates and so that the plates arerdetachably connected to each other. The looped portions of the wire may consist of a series of oppositely disposed open loops Ywhich are adapted to serve as heating elements, being located near the inner surface of the plates whereby the maxi mum amount of heat is supplied to the chamber 15 and whereby a substantial body'of heat refractory material is disposed between the heating wire and the heat insulating clay 17. As illustrated in Fig. 8, the backs of each of the muilie plates are providedV with recesses or grooves 25 to accommodate the twisted wire sections 22. Preferably the mulile plates are arranged to have their vertical edges in slightly tapered relation to each other whereby the plates may be quick ly removed from the muftle by detachment of muliie 'furnace 'descr'ibed above.

the wire 20 and whereby they may be located in accurate juxtaposition with a wedge-like action when they lare assembled vin the furnace.

The cover 7 is provided with a suitable filler of heat insulating substance such as clay, which is 'adapted to reflect the heat from the nflle plates. An elongate, s`u`bstantially cylindrical opening 26 extends through the cover and filler with a hinged cap 27 located at its outer end. This opening with the cooperating cap is adapted to permit the dentist lto observe co'nc'litio'n's Within the fire chamber. Suitable connections "29 may also be provided in :the cover for the installation of pyrometer if the same 'is desired.

rAt one .s idelof the 'base member 1 is disposed l'a suitable stand 30 pivotally mounted on :the arm 3l which is itself pivotally mounted on the upright 32 aligned with one leg 2"'of 'base l. The stand 30 is provided with a flight `"cover 33 of alu'n'i'i'nun'i or the like.

'It is `to beunderstood that porcelain dentures or the like may 'be 4baked in the A denture is prepared 1and may be placed upon` a clay tray o'r the like and vlocated within the ine chamber l5. The Icover -7 is then located over :the chamber, the frheostat being gradually 'cut out by the roperation of handle 5 u'ntil the "platinum 1resistance`,wif1'e 2O 'is given itsfmanimum temperature. The mullie'plates 16 are heated tota ihigh ten'iperature,the ltemperature within Ithe chamber being"gradu-v ally 'less toward its o'uter wall due to the locatin of the wire close to the inner `sufrfa'ce 'of the mu'flie lplates and to V"the fthickness o'f Yheat insulating material. Uniform disposition of the inutiles around thefcentral chamber 'also ensures the maximum thermal eliiciency and `rconsistency :of Ioperation of the "fur'na'ce. if desi-red AJhe 'cover :plate `27 may be opened s'o lthat thedentist may view thecondition'ofjthe denture'during the baking operation WVhen the 'baking `operation has 'been cdmpletech the cover 7 may be lifted, the arm 8 `being thrown over, and the "denture "may be removed vandlocated upon the stand 30, being covered with member 33 to permit uniform and gradual coolinv;

tfis 'now 'evident that a porcelain furnace has 'been provided which Ais comparatively simple vand inexpensive, which is 'provided with mu'flle plates which may be made interchangeable and may be 'quickly replaced either in 'series or individually land that the device has been designed ywith a careful attention 'to thermal ei'liciency, uniformity of workingoperation's, and convenience to thegoperator.

We claim:

IHA muiiie furnace comprising 'an outer y."haracteriz'ed yby the fact lthat the 'plates are secured to each yother by project-ing pieces of pliable wire bent :into 'engagement with similar pieces upon adjoining lunits and thfns comprising electrical connect-ions fo'r heating means. g

t. The A'subject matter off *claim l further characterized by Vthe Afact Ithat the platcs are provided with looped wire port-ions embedded 'therein to comprise electric heating means 4'and that projections of the looped wire of `each plate are twisted into engagement withsimilar projec'tion'sof'one orinoie adjoining plates Yto fform 'mechanical an'd electrical connections between -tlie plates.

5. The subject 'mattei' "of cla-iin l further characterized'by the fact that fthe plates *are providedA 'with looped wire portions 'em'- bedded therein lto cdinprise electric heating means and thatl projections lof 4the looped wire Aof each plate "are twisted into #engagement with similar projections 'oif adjoining plates to form mechanical-and electrical connections between the plates, Tportions of 'the plates 1being recessed to accommodate said twisted wire portions.

6. The subject lmatter of claim l *further characterized by the fact xthat "the lplates are 'connected to 'each other by wire forming electrical connections for "the `heating means and that wire portions which vconnected with ran external source of energy comprise means detachably holding the l'seriesof plates in the furnace. j

7. The subject matter of claim l further characterized 'by the fact that 'the Y*plates have their juxtaposed edges ltapered and that vthe adjoiningfaces ofthe "layer of heat insulating material are correspondingly xinclined 'toward eachother, whereby the 'plates may be located within the `fiurnace'in firm contacting Vrelation with each lether.

8. A :inutile furnace comprising a 'casing having an lopening therein 'through which articles to beheated maybe insertedandiremoved, the surface of saidcasing 'adjoining said opening being ltapered, 'lining in lsaid casing of refractory material cmprising 4a seriesof abutting plates removably mounted around the inside wall ofthe casing adjacent said opening, the surface'sof said plates Signed by me at Boston, Massachusetts, i this 16th day of April, 1926.

being tapered adjoining the tapered portion of the said casing and the adjoining edges of the said plates being mutually tapered, Y WALTER G. BRIDGE. 10 resistance Wire mounted in the interior of Signed by me at Boston, Massachusetts, v the said plates, the plates being slidable this 9th day of April, 1926.

through said opening when the said closure is opened. WILLIAM A. PERVIER. 

